Method for transition between distributed transmission and localized transmission

ABSTRACT

Provided is a method for transitioning between a distributed transmission mode and a localized transmission mode, including transmitting, by a Base Station (BS), a measurement control message to a User Element (UE), wherein the UE makes corresponding measurement and transmits a required measurement report message to the BS and the BS transmits a transition indicator message of new mode to the UE based on measurement report message sent from the UE; and commencing CQI reporting and a downlink transmission of a new mode between the UE and the BS. The BS can choose a more appropriate transmission mode for the downlink transmission based on changing characteristics of the channel in the time domain and the frequency domain.

FIELD OF THE INVENTION

The present invention relates to radio communication system with localized data transmission mode and distributed data transmission mode, especially to the transition between the two transmission modes.

DESCRIPTION OF THE PRIOR ART

Now, the 3^(rd) Generation Mobile Communication System Partnership Project (referred to as 3GPP) standardization organization has commenced on Long-term Evolution (referred to as LTE) to existing system criteria. Among numerous physical layer transmission techniques, OFDM (Orthogonal Frequency Division Multiplex) becomes a challenging one in all downlink solutions, for it bears such advantages as higher spectrum efficiency and lower processing complexity.

In nature, OFDM is a kind of multi-carrier modulation communication technique. Its basic principle is to divide a high rate data stream into multiple low rate data streams to transmit via a group of orthogonal sub-carriers simultaneously. Because of the nature of multi-carrier, the OFDM technique bears superior performance in many aspects. (1) A remarkable superiority of the OFDM technique lies in that: inter-symbol interference (ISI) can be completely eliminated in the case that the channel delay is less than the length of CP (cyclic prefix, which is introduced in by adding guard spacing to each symbol), for data is transmitted through multiple sub-carriers in parallel and the length of symbol in each sub-carrier is correspondingly increased but with no sensitivity to channel delay. In this way, every sub-carrier experiences a flat fading channel. (2) The OFDM technique bears high spectrum utility factor. In frequency domain, OFDM signals overlap actually. This kind of overlap improves spectrum utility factor in great extent. (3) The OFDM technique bears strong ability in anti-narrowband interference or resisting frequency selective fading. Through channel coding and interleaving, the frequency diversity effect and the time diversity effect can be achieved in OFDM so that either narrowband interference or frequency selective fading can be effectively resisted. (4) In the technique of OFDM, the modulation can be realized through the base-band IFFT, while IFFT/FFT bears available fast calculation method and can be conveniently implemented in a DSP chip and hardware structure.

There are two transmission modes in OFDM radio transmission system: localized transmission mode and distributed transmission mode.

So called localized data transmission means that the data is transmitted in sequential sub-carriers of the localized sub-band, and the network end will specify effective modulation coding method for its data transmission to realize adaptive modulation coding based on channel quality between the BS and the UE, thus increase data transmission throughput. And distributed transmission mode means that the UE uses comb-like sub-carrier to transmit over the whole frequency band, making the sub-carriers that transmit data be distributed in the whole frequency band as much as possible, thus maximizing frequency diversity gain. Usually localized data transmission mode which can use adaptive modulation coding and frequency scheduling has greater transmission gain, but to some channels of fast changing speed, channel condition predicted at some time can't reflect that of the next time, therefore localized transmission is hard to implement. So, the distributed data transmission mode is often adopted for data transmission with the help of the frequency diversity gain.

During the process of downlink data's transmission:

In the case of localized transmission mode, a UE (user equipment) will measure the channel quality for each sub-band in the system frequency band, then reports the measured Channel Quality Indicator (CQI) of each sub-band to the base station (BS). Having received the CQIs, BS determines whether to allocate frequency resource to the UE or not, and which localized frequency bands to be allocated to UE for data transmission, according to the reported CQI from each UE and the system current load. During the process of data transmission, it is necessary for a UE to go on to measure the channel quality for each sub-band in the system frequency band and transmit the measured CQI to the base station so as to achieve the goals of frequency scheduling and adaptive modulation coding (AMC) for data transmission. In this way, maximum throughput of data transmission can be reached.

And in the case of distributed transmission mode, a UE will measure the mean channel quality of the entire system frequency band, then report the unique mean CQI to the base station. Having received this mean CQI, BS determines whether to allocate distributed frequency resource to the UE or not according to the reported CQI from each UE and the system current load. And during the process of data transmission, it is also necessary for a UE to go on to measure the mean CQI of the entire system frequency band and transmit the measured CQI to the base station so as to achieve the goals of frequency scheduling and adaptive modulation coding (AMC) for data transmission. In this way, maximum throughput of data transmission can be reached.

From the descriptions above, it's seen that: in localized transmission mode, the contents of the measurement report sent to BS from UE are sub-bands' CQIs, and in distributed transmission mode, a UE only sends the average CQI to BS. Therefore, the number of bits necessary for the transmission of CQI information in localized transmission mode is far greater than that in distributed transmission mode.

In the LTE system, the system will choose appropriate transmission mode for data transmission between the BS and the UE based on the channel condition between them. When the channel condition between the BS and the UE changes, the transition between localized transmission and distributed transmission will probably happen.

There is a transition between the two transmission modes in existing IEEE802.16E radio transmission technology. Thereinto, signalling flowchart of the process of transition from distributed transmission to localized transmission is shown in FIG. 1. The implementation steps are:

The UE checks the maximum value of standard deviation in time domain of SNRs measured in all the sub-carriers, if the maximum value keeps lower than an appointed threshold for a period of time and the mean SNR of the whole frequency band is larger than an appointed threshold, then the UE transmits 101 transition indicator from distributed transmission mode to localized transmission mode to the BS. After the BS has received the transition indicator, it will transmit 102 channel measurement report request (REP-REQ) to the UE. After the UE has received the measurement report request, it will transmit 103 channel measurement report response (REP-RSP) to the BS, the REP-RSP message contains channel quality indicator of 5 sub-frequency bands with best channel quality. From the beginning of next frame after transmitting REP-RSP message, the UE will transmit 104 time domain difference CQI report of the chosen frequency bands to the BS. Afterwards the BS will transmit 105 localized channel allocation to the UE based on CQI reported by the UE, and then transmit 106 localized data transmission to the UE.

Signalling flowchart of process of transition from localized transmission mode to distributed transmission mode is shown in FIG. 2, the implementation steps are:

The UE checks the maximum value of standard deviation in time domain of SNRs measured in all the sub-carriers, if the maximum value is higher than an appointed threshold for a period of time, then the UE will transmit 201 transition indicator from localized transmission mode to distributed transmission mode to the BS, then the UE will transmit 202 mean CQI report of the whole frequency band to the BS. Afterwards the UE will repeatedly transmit 201 transition indicator from localized transmission mode to distributed transmission mode and 202 mean CQI report of the whole frequency band, until the BS transmits 203 distributed channel allocation to the UE. Afterwards the BS will transmit 204 distributed data transmission to the UE.

It can be seen from data transmission mode transition process method in IEEE802.16E that if the maximum value of standard deviation of SNRs measured in all sub-frequency bands in time domain is comparatively large, then distributed transmission is suitable for the UE, and if the maximum value of standard deviation of SNRs measured in all sub-frequency bands in time domain is comparatively small and the mean SNR of the whole frequency band is larger than an appointed threshold, then localized transmission mode is the suitable transmission mode for the UE. As the high speed moved UE's time domain channel variation has comparatively large variance, and low speed moved UE's time domain channel variation has comparatively small variance, according to IEEE802.16E specification, distributed data transmission is suitable for high speed moved UE, and for low speed moved UE, if the mean SNR of its whole frequency band is high, then localized data transmission is suitable for it.

As for localized transmission mode, as more uplink signalling is needed to transmit several sub-bands' channel quality indicators (CQI), the corresponding uplink signalling load is heavy. However data transmission in flat fading channel condition, localized data transmission can't acquire much selective frequency gain compared to distributed data transmission, because SNRs of all sub-carriers are basically the same no matter they are localized data transmission carriers or distributed data transmission carriers, thus their adaptive modulation coding gains are basically the same no matter they use distributed transmission or localized transmission. But localized transmission needs CQI report of uplink multi-bands, thus introducing heavier signalling load compared to distributed transmission. It can be seen that for flat fading channel, even it is low speed moved UE and the mean SNR is comparatively high, distributed data transmission can still acquire the same selective frequency gain as that of localized data transmission, and its uplink signalling load is small, thus distributed data transmission mode is more suitable.

Besides, the standardized method of 3GPP defines it is the network that controls transmission method of the UE, not the UE that decides transition of data transmission mode. Therefore the mode transition in IEEE802.16E is not suitable for data transmission mode transition in 3GPP LTE.

Therefore some improvements can be made towards mode transition method in IEEE802.16E, making the UE use more suitable transmission mode to transmit data.

In order to optimize the above mentioned process of mode transition, some new measurement report and measurement report process need to be defined. These measurement controls and reports can be transmitted through RRC signalling and physical layer signalling.

There are physical layer interface and also interface to control radio resource between the UE and the BS, such as RRC protocol defined in 3GPP. The BS configures network resource used by the UE through the interface protocol, and control's UE's functions such as measurement, handover, etc. Physical layer interface between the UE and the BS is mainly responsible for physical signal exchange, such as CQI report of existing system. CQI report is implemented through channel structure defined by given physical channel, such as channel structure defined in 3GPP TS 25.211, or channel structure defined by itself.

SUMMARY OF THE INVENTION

Based on the above mentioned problems, the present invention provides a data transmission mode transition method, the BS can indicate UE to transmit the needed measurement report based on channel condition of data transmission, and indicate the UE of its transmission mode based on this measurement report.

In order to achieve the above goal, a method of transition between distributed transmission mode and localized transmission mode includes steps:

a) The BS transmits measurement control message to the UE;

b) The UE makes corresponding measurement and transmits the required measurement report message to the BS;

c) The BS transmits transition indicator message of new mode to the UE based on measurement report message sent from the UE;

d) CQI report and downlink transmission of new mode between the UE and the BS begins.

The BS of the present invention can choose more appropriate transmission modes for downlink transmission based on changing characteristics of the channel in time domain and frequency domain. When choosing transmission mode, it also considers changing characteristics of frequency domain, whereas the traditional method is to choose transmission mode only according to changing characteristics of time domain, the new method allows downlink transmission to use distributed transmission under the channel condition similar to flat fading, thus reducing uplink signalling overhead without reducing transmission gain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows signalling flowchart of process of transition from distributed transmission to localized transmission in IEEE802.16E;

FIG. 2 shows signalling flowchart of process of transition from localized transmission to distributed transmission in IEEE802.16E;

FIG. 3 shows signalling flowchart of process of transition between distributed transmission and localized transmission according to present invention

FIG. 4 shows signalling flowchart of process of transition from distributed transmission to localized transmission according to the present invention;

FIG. 5 shows signalling flowchart of process of transition from localized transmission to distributed transmission according to the present invention;

FIG. 6 shows BS's operation flowchart of process of transition from distributed transmission to localized transmission according to the present invention;

FIG. 7 shows UE's operation flowchart of process of transition from distributed transmission to localized transmission according to the present invention.

FIG. 8 shows BS's operation flowchart of process of transition from localized transmission to distributed transmission according to the present invention;

FIG. 9 shows UE's operation flowchart of process of transition from localized transmission to distributed transmission according to the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention gives the transition method between localized data transmission and distributed data transmission in downlink transmission, signalling flowchart of process of transition implemented in the method is shown in FIG. 3, the process includes following steps:

The BS can judge whether the UE has converted its transmission mode according to UE's service type information and the BS's information such as measurement. When the BS judges some measured information reported by the UE should be used to judge transmission mode transition, then the measurement to be done by the UE could be configured, radio resource control signalling measure control message 301 can be transmitted to the UE, which includes the measurement to be taken by the UE (such as measured value of selectivity in frequency domain to reflect downlink channel fading) and measurement report condition. When the BS indicates the measurement report condition, it can indicate a measurement report threshold to the UE, and it can also indicate period of the UE reporting measurement report. After the UE has received the message, it measures according to the indicator, specific measurement differs according to the measurement type. When UE's measurement satisfies BS's report condition, the UE will transmit measurement report message 302 to the BS, which can contain specific measured value, or event type measurement report or other information. When measurement report is event type, a feasible method is that the UE reports the event to the BS when its measured value is higher than some threshold or lower than some threshold. Based on measured value or measure event reported from the UE, the BS can decide UE's action in detail, and transmit new mode transition indicator 303 to the UE, indicating the UE to make mode transition or state transition. After the UE has received transition indicator, the CQI report and downlink transmission 304 of new mode between the UE and the BS begins.

In the above mentioned process, 301, 302 and 303 are all radio resource control signalling, and CQI report in 304 is physical layer signalling.

What needs to be mentioned is that the downlink localized transmission mode mentioned in the present invention only means CQI report method of the UE in this mode, which is localized CQI report, namely reporting CQI of several sub-frequency bands, it is suitable to transmit data in localized resource, but it does not exclude that the BS allocates data transmission to some distributed resource in some sub-frames although the UE transmits localized CQI report in the transmission process of this mode. In the same way, the downlink distributed transmission mode means the CQI report transmitted by the UE is unitary in the frequency band, it is suitable to be transmitted in distributed resource, but in the same way it does not exclude in the transmission process of the mode, although the UE transmits distributed CQI report, the BS can allocate data transmission to some localized resource in some sub-frames.

There are two processes of downlink transmission transition between localized data transmission and distributed data transmission, one is process of transition from distributed transmission to localized transmission, another is process of transition from localized transmission to distributed transmission.

Thereinto, signalling flowchart of process of transition of distributed transmission to localized transmission is shown in FIG. 4, the process includes following steps:

The BS monitors change in time domain of the UE's uplink transmission channel quality, if the change is slow, it will transmit 401 measure control signalling to the UE, indicating the UE to report measurement report that reflects frequency domain selective fading degree in downlink channel and its report condition. When the BS indicates measurement report condition, it can indicate a measurement report threshold to the UE, or period of UE reporting measurement report. After the UE has received the measure control signalling, it will begin to measure frequency domain selectivity in its downlink channel, and when the report condition is satisfied, it will transmit 402 measurement report to report the measured fading's selectivity value in frequency domain in downlink channel or event that reflects fading's frequency domain selectivity change in downlink channel to the BS. After the BS has received frequency domain selectivity report or event report from the UE, it will judge whether to convert the UE's downlink transmission from distributed transmission to localized transmission based on its fading's frequency domain selectivity change degree or the received event report. If it does, then the BS will transmit to the UE 403 transition indicator from distributed transmission to localized transmission.

After the UE has received 403 transition indicator, it will begin to transmit to the BS 404 localized CQI report, transmit CQI report of several CQI report frequency sub-bands to the BS. After the BS has received localized CQI report, it will make channel allocation for the UE based on CQIs of various CQI report sub-frequency bands, and transmit to the UE 405 localized channel allocation signalling, indicating which frequency sub-bands are used to transmit data to the UE. Afterwards, the BS will transmit to the UE 406 localized data transmission.

Signalling flowchart of process of transition from localized transmission to distributed transmission is shown in FIG. 5, the process includes following steps:

The BS monitors change in time domain of the UE's uplink transmission channel quality, if the change is fast, namely the change degree in time domain of UE's uplink channel measured by the BS satisfies an appointed condition, the BS will transmit to the UE 503 transition indicator from localized transmission to distributed transmission. And if the change is slow, the BS will continue judging whether CQIs of several CQI report sub-frequency bands sent from the UE to the BS can reflect frequency domain selective fading degree of downlink channel, namely whether the number of sub-frequency bands in localized CQI report can reflect frequency domain selective fading degree of the whole frequency band, if it is, then the BS will decide frequency domain selective fading degree based on localized CQI report, and judge whether to transmit 503 transition indicator from localized transmission to distributed transmission to the UE based on the decided frequency domain selective fading degree. But if the localized CQIs transmitted from the UE to the BS is CQIs of partial CQI report sub-frequency bands and can't be used to judge the frequency domain selective fading degree of the whole frequency band, the BS will transmit to the UE 501 measure control signalling, indicating the UE to report measurement report that reflects frequency domain selective fading degree of downlink channel, and its report condition. When the BS indicates measurement report condition, it can indicate a measurement report threshold value to the UE, or can indicate period of UE reporting measurement report. After the UE has received the measure control signalling, it will begin to measure frequency domain selectivity in its downlink channel, and when the report condition is satisfied, it will transmit to the BS 502 measurement report to report its measured fading's selectivity value in frequency domain in downlink channel or event that reflects fading's frequency domain selectivity change in downlink channel. After the BS has received frequency domain selective report or event report from the UE, it will judge whether to convert the UE's downlink transmission from localized transmission to distributed transmission based on its fading's frequency domain selectivity change degree or the reported event. If it does, then the BS will transmit to the UE 503 transition indicator from localized transmission to distributed transmission.

After the UE has received 503 transition indicator, it will transmit to the BS 504 distributed CQI report, transmit to the BS mean CQI report of the whole frequency band. After the BS has received distributed CQI report, it will allocate channel for the UE based on the reported CQI value, and transmit to the UE 505 distributed channel allocation signalling, indicating which distributed sub-frequency bands are used to transmit data to the UE. Afterwards, the BS will transmit to the UE 506 distributed data transmission.

In the following two transition processes, the specific operation steps of the BS and the UE are:

In the process of transition of distributed transmission to localized transmission, the operation flowchart of the BS is shown as FIG. 6, its steps are as follows:

In the process that the BS transmits distributed data transmission 602 to the UE, it will execute 603 monitoring the change in time domain of UE's uplink channel quality, then make the judgment 604 whether the change of time domain of the UE's uplink channel is slow, if it isn't, go on with distributed transmission and monitoring, if it is, the BS will transmit measurement control signalling 605, indicating the UE to report measurement report that reflects frequency domain selective fading degree of downlink channel and its report condition. When the BS indicates measurement report condition, it can indicate a measurement report threshold value to the UE, or can indicate period of UE's measurement report. Then it begins to receive measurement report that reflects frequency domain selective fading degree of downlink channel or event that reflects changing degree 606 transmitted by the UE, and judges 607 whether the transition condition from distributed transmission to localized transmission is satisfied, if it isn't satisfied, then go on to receive 606 measurement report, if it satisfies transition condition, then executes 608 transmitting to the UE transition indicator from distributed transmission to localized transmission. Afterwards it begins to receive localized CQI report 609 sent from the UE, then allocates channel for the UE based on the reported CQI values of various frequency bands, and transmits to the UE localized channel allocation indicator 610. After that it can transmit localized data transmission in the allocated channel 611 to complete the process of transmission mode transition.

In the process of transition of distributed transmission to localized transmission, UE's operation flowchart is shown as FIG. 7 with steps as follows:

When the UE receives measurement control signalling 702 indicating it to report frequency domain selectivity measurement report of downlink channel fading and report condition, the UE begins to make corresponding measurement 703. Then it judges 704 whether the report condition is satisfied, if it isn't, it goes on with measurement and judgment; if it is, then it executes 705 transmitting fading's frequency domain selectivity measurement report or transmitting event that reflects frequency domain selectivity change to the BS. Afterwards, 706 it monitors whether it has received mode transition instruction from distributed transmission to localized transmission sent from the BS, if it hasn't, then goes on with measurement and report; if it receives mode transition instruction, then it will 707 transmit localized CQI report to report CQIs of several CQI report sub-frequency bands to the BS. Then, 708 it receives localized channel allocation signaling sent from the BS, knowing which sub-frequency bands the BS will transmit data in, then it can 709 receive localized data transmission in appointed frequency bands, thus completing transmission mode transition process.

In process of transition from localized transmission to distributed transmission, operation flowchart of the BS is shown as FIG. 8, with steps as follows:

In the process that the BS transmits localized data transmission 802 to the UE, it will execute 803 monitoring change in time domain of the UE's uplink channel quality, then judges 804 whether the change in time domain of the UE's uplink channel is slow, if it isn't, then it transmits to the UE transition indicator 809, indicating it to convert from localized transmission to distributed transmission. If it is, the BS will continue judging whether it can judge fading's frequency domain selectivity based on current CQI report of localized transmission 805, if it can, it judges whether the condition to convert from localized transmission to distributed transmission is satisfied based on channel fading's frequency domain selectivity 808; If it isn't, then the BS will transmit measure control signalling to the UE 806, indicating the UE to report downlink channel fading's frequency domain selectivity measurement report and report condition. When the BS indicates measurement report condition, it can indicate a measurement report threshold value to the UE, and can also indicate period of UE reporting measurement report. Then it receives measured value of downlink channel fading's frequency domain selectivity sent from the UE or measurement report of event that reflects downlink channel fading's frequency domain selectivity change degree 807. Afterwards it judges whether the condition to convert from localized transmission to distributed transmission is satisfied based on channel fading's frequency domain selectivity measurement report or event report 808.

Execute the judging 808, if the judging result is no, then the BS will continue executing step 805; And if the judging result is yes, the BS will transmit to the UE transition indicator 809, indicating it to convert from localized transmission mode to distributed transmission mode. Then, the BS will receive distributed CQI report transmitted from the UE 810, and transmit to the UE channel allocation indicator of distributed transmission based on the reported CQIs 811, finally it will transmit distributed transmission to the UE in indicated channels 812, thus completing the transition from localized transmission mode to distributed transmission mode.

In the process of transition from localized transmission to distributed transmission, operation flowchart of the UE is shown as FIG. 9, with steps as follows:

When the UE is in the process of localized transmission, it monitors whether there is measurement control signalling coming from the BS 902, judges whether the BS requires it to report measurement report of downlink channel fading frequency domain selectivity. If it doesn't, then the UE will continue monitoring whether there is transmission mode transition indicator from the BS 906. If there is, then it will execute 903 measuring downlink channel fading's frequency domain selectivity. Afterwards it judges 904 whether the report condition is satisfied, if it isn't satisfied then continue executing step 903, if it is satisfied then it executes 905 transmitting to the BS downlink channel fading's frequency domain selectivity measurement report or event report that reflects fading's selectivity changing degree in frequency domain, afterwards executes 906, judges whether there is transmission mode transition indicator coming from the BS 906.

Executes the judging 906, if the judging result is no, then the UE will execute step 902, and if the judging result is yes, then it will transmit to the BS distributed CQI report 907, then receive distributed channel allocation indicator sent from the BS 908, finally it can receive distributed transmission sent from the BS in the allocated distributed channel 909, thus completing the transition from localized transmission to distributed transmission.

IMPLEMENTATION EXAMPLE

To clearly illustrate the method proposed in the present invention, an implementation example is given in the following.

Transition example from distributed transmission to localized transmission is given first:

Suppose the UE's current downlink data transmission is distributed transmission, and the UE is a low speed moved UE, the change in time domain of its channel is slow. During the transmission, the BS will monitor change in time domain of the UE's uplink transmission channel quality, a feasible method is that the BS measures variance of SNRs in uplink transmission sub-carriers. If during a period of time, the measured variance of SNRs is lower than an appointed threshold, then the BS can judge that the change in time domain of the UE's channel is slow, the LYE is low speed moved UE. In such channel condition, localized transmission may be the suitable downlink transmission mode for the UE.

However, as for flat fading channel, as distributed transmission can acquire the same transmission gain as localized transmission, and the corresponding uplink report CQI signalling load is relatively light, therefore in flat fading channel, distributed transmission is the optimal transmission method. Therefore the further judgment needs to be done based on the UE′ downlink channel fading's frequency domain selectivity, therefore the BS transmits to the LYE measure control signalling, requiring the UE to report downlink channel fading's frequency domain selectivity measurement report. In the mean time when the BS requires the UE to report the measurement report, it can also give the corresponding measurement report condition. For example, it gives the threshold of the measurement report, when the measured value is larger than the threshold, the UE will transmit to the BS the measurement report, event report, indicating comparison result of the measured value and threshold; or give an appointed report period, for example, the BS gives the report period of 10 ms, then the UE will transmit measurement report to the BS every 10 ms to report the measured value.

After the UE has received the measure control signaling to require it to report downlink channel fading's frequency domain selectivity measurement, the UE will begin to take such measurement. The implementation example shows that the measured value that describes downlink channel fading's selectivity in frequency domain is maximum CQI difference CQI_difference_max of various CQI report sub-frequency bands, namely the difference of the maximum CQI subtracting the minimum CQI of all CQI report sub-frequency bands. Therefore the UE can measure SNRs of all CQI report sub-frequency bands, and judge CQI value of all sub-frequency bands based on this, and calculate CQI_difference_max value to be reported. Then the UE will refer to measurement report condition given by the BS. In the implementation example, measurement report condition is used to judge whether the measured CQI_difference_max value is larger than report threshold indicated by the BS.

When report condition is satisfied, the UE will transmit to the BS event report, notifying the BS the measured CQI_difference_max value has exceeded report threshold indicated by the BS. Illustrating there is relatively large frequency domain selective fading in downlink channel, using localized transmission will acquire relatively large scheduling gain. In this way, the BS will report to the UE indicating signalling to convert from distributed transmission to localized transmission based on this event.

After the UE has received transition indicator signalling, it will transmit to the BS localized CQI report to report CQI values of several sub-frequency bands. The BS will allocate localized channel for the UE based on localized CQIs reported by the UE, afterwards it will make localized transmission in these localized channels, thus completing process of mode transition from distributed transmission to localized transmission.

The following shows transition example from localized transmission to distributed transmission:

Suppose current UE's downlink data transmission is localized transmission, and the system's total number of CQI report sub-frequency bands is 8.

The BS first will monitor change in time domain of UE's uplink transmission channel quality, for example, monitor variance of SNRs in uplink transmission sub-carriers.

If the variance is larger than an appointed value for a period of time, then it illustrates that the UE is a high speed moved UE, its appropriate transmission mode is distributed transmission, therefore the BS will transmit transition indicator from localized transmission to distributed transmission signalling to the UE directly.

If the variance is lower than an appointed value for a period of time, then it illustrates that the UE is a low speed moving UE, its downlink channel fading's selectivity in frequency domain needs to be monitored sequentially.

Now the UE's localized CQI report method needs to be considered, if the UE's localized CQI report is whole frequency band's CQI report, namely that the UE reports CQI values of every CQI report frequency sub-band to the BS, then the BS no longer needs any other additional measurement report, and can judge directly downlink channel fading's selectivity in frequency domain based on localized CQI report directly, and judges whether to transmit transition indicator from localized transmission to distributed transmission to the UE based on this.

But in current localized CQI report methods, many of which only report CQIs of several sub-frequency bands with best channel quality, in this way based on these CQI reports of these sub-frequency bands, the BS is often hard to judge frequency domain selective fading degree of the whole frequency band. Suppose in the implementation example, the UE only reports 3 sub-frequency bands with best channel quality out of the 8 sub-frequency bands, then in order to acquire downlink channel fading's frequency domain selectivity, the BS needs measurement report that reflects downlink channel fading from the UE. At this time, the BS will transmit measure control signaling to the UE, indicating report threshold of CQI_difference_max and reporting maximum report CQI difference CQI_difference_max of CQI report sub-frequency bands and event report of the indicated report threshold comparison result. After the UE has received this indication, it will measure CQI value of all sub-frequency bands, and calculate CQI_difference_max, and transmit corresponding event report to the BS when it finds that the CQI_difference_max is lower than report threshold. After the BS has received event report, it get to know the frequency domain selective fading in downlink channel is relatively small, the channel is nearly flat fading channel, therefore distributed transmission mode is more appropriate, therefore the BS will transmit mode transition indicator from localized transmission to distributed transmission to the UE. After the UE has received this mode transition indicator, it will transmit distributed CQI report to the BS, and the BS will allocate distributed transmission channel for the UE based on distributed CQI report sent from the UE, afterwards makes distributed transmission in the allocated distributed channel, thus completing mode transition process from localized transmission to distributed transmission. 

1. A method of transition between distributed transmission mode and localized transmission mode includes: a) transmitting, by a Base Station (BS), a measurement control message to a User Equipment (UE); b) performing by the UE, a corresponding measurement and transmits a required measurement report message to the BS; c) transmitting, by the BS, a transition indicator message of a new mode to the UE based on the measurement report message sent from the UE; d) performing Channel Quality Indicator (CQI) reporting and a downlink transmission of the new mode between the UE and the BS begins.
 2. The method according to claim 1, wherein the new mode contains a distributed transmission mode and a localized transmission mode.
 3. The method according to claim 2, wherein the distributed transmission mode reports a single CQI of the whole frequency band to the BS for the UE.
 4. The method according to claim 2, wherein the localized transmission mode reports several CQIs of several sub-frequency bands to the BS for the UE.
 5. (canceled)
 6. (canceled)
 7. (canceled)
 8. The method according to claim 1, wherein the measurement control message contains a report condition to be measured by the UE.
 9. The method according to claim 1, wherein said measurement control message in step a) contains threshold indicated by the BS to the UE.
 10. The method according to claim 1, wherein said measurement control message in step a) contains period of measurement report indicated by the BS to the UE.
 11. The method according to claim 1, wherein said measurement report sent from the UE in step b) contains measurement report that reflects downlink channel fading selectivity in frequency domain.
 12. The method according to claim 1, wherein said measurement report sent from the UE in step b) is event type.
 13. The method according to claim 12, wherein said event reflects comparison result of measured value measured by the UE and threshold indicated by the BS. 